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Subject: Re: [PATCH v3] mm, slub: change run-time assertion in kmalloc_index()
 to compile-time
To:     Nathan Chancellor <nathan@kernel.org>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc:     akpm@linux-foundation.org, iamjoonsoo.kim@lge.com,
        rientjes@google.com, penberg@kernel.org, cl@linux.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        naresh.kamboju@linaro.org, clang-built-linux@googlegroups.com,
        linux-next@vger.kernel.org, ndesaulniers@google.com,
        lkft-triage@lists.linaro.org, sfr@canb.auug.org.au, arnd@arndb.de,
        Marco Elver <elver@google.com>
References: <20210511173448.GA54466@hyeyoo> <20210515210950.GA52841@hyeyoo>
 <41c65455-a35b-3ad3-54f9-49ca7105bfa9@suse.cz>
 <YKC9CeAfw3aBmHTU@archlinux-ax161> <20210518003859.GC80297@hyeyoo>
 <a1287a21-bcbb-77ed-c88d-f5890b785213@kernel.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <71416382-2e4c-5e03-df9c-265fda41c2de@suse.cz>
Date:   Tue, 18 May 2021 11:28:17 +0200
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On 5/18/21 2:43 AM, Nathan Chancellor wrote:
> On 5/17/2021 5:38 PM, Hyeonggon Yoo wrote:
>> On Sat, May 15, 2021 at 11:34:49PM -0700, Nathan Chancellor wrote:
>>> This should work I think:
>>
>> compiled well with clang-10.0.1, clang-11.0.0,
>> and gcc-10.2.0 with x86_64 default config.
>>
>> is the condition CONFIG_CLANG_VERSION > 110000,
>> not including 110000 it self?

Good spot.

> Ah sorry, that should definitely be >= :(
> 
> That is what I get for writing an email that late... in reality, it probably
> won't matter due to the availability of 11.0.1 and 11.1.0 but it should
> absolutely be changed.
> 
> I have not given Nick's patch a go yet but would something like this be
> acceptable?

Yes.

> If so, did you want me to send a formal fixup patch or did you want
> to send a v4? I have no personal preference.

At this point a fixup is the usual way. Andrew might squash it to the original
patch (also with Marco's fixup) before sending to Linus.

>>> diff --git a/include/linux/slab.h b/include/linux/slab.h
>>> index 9d316aac0aba..1b653266f2aa 100644
>>> --- a/include/linux/slab.h
>>> +++ b/include/linux/slab.h
>>> @@ -413,7 +413,7 @@ static __always_inline unsigned int
>>> __kmalloc_index(size_t size,
>>>       if (size <=  16 * 1024 * 1024) return 24;
>>>       if (size <=  32 * 1024 * 1024) return 25;
>>>   -    if (size_is_constant)
>>> +    if ((IS_ENABLED(CONFIG_CC_IS_GCC) || CONFIG_CLANG_VERSION > 110000) &&
>>> size_is_constant)
>>>           BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()");
>>>       else
>>>           BUG();
>